Air control valve for a pneumatic brake system

ABSTRACT

A failsafe, foolproof control valve for a tractor-trailer air brake system which, among its other features, permits the tractor brakes to remain in a parked position while the trailer system is being pressurized. The control valve includes four ports, two of which communicate with a first valve chamber and the other two communicate with a second valve chamber. A spring biased first plunger is disposed within the first chamber and a manually operable second plunger extends within the second chamber. Movement of the second plunger establishes several operating modes of the valve to provide various fluid flow paths between the ports in a predetermined manner. At least one of these modes automatically repositions the second plunger to its normal operating mode after the trailer system has been optionally pressurized by actuation of a conventional park valve.

United States Patent 11 1 Darling 1451 Sept. 30, 1975 AIR CONTROL VALVEFOR A PNEUMATIC BRAKE SYSTEM [75] Inventor: Harold Durllng, Elsie. Mich.

[731 Assignee: Midland-Ross Corporation.

Cleveland, Ohio 221 Filed: Dec.11,1974

21 Appl.No.:53l,644

Related US. Application Data [62] Division of Ser. No. 449.707. March11, 1974.

Primary Evztminer-Duane A. Roger Attorney. Agent. or Firm-Frank .l.Nawalanic 5 7 1 ABSTRACT A failsafe, foolproof control valve for atractor-trailer air brake system which, among its other features,permits the tractor brakes to remain in a parked position while thetrailer system is being pressurized. The control valve includes fourports, two of which communicate with a first valve chamber and the othertwo communicate with a second valve chamber. A spring biased firstplunger is disposed within the first chamber and a manually operablesecond plunger extends within the second chamber. Movement of the secondplunger establishes several operating modes of the valve to providevarious fluid flow paths between the ports in a predetermined manner. Atleast one of these modes automatically repositions the second plunger toits normal operating mode after the trailer system has been optionallypressurized by actuation of a conventional park valve.

8 Claims, 6 Drawing Figures US. Patent Sept. 30,1975 Sheet 2 of33,909,069

US. Patent Sept. 30,1975 Sheet 3 of3 3,909,069

FIG. 5

FIG.6

AIR CONTROL VALVE FOR A PNEUMATIC BRAKE SYSTEM This is a division ofapplication Ser; No. 449,707, filed Mar. 11, I974.

This invention relates generally to a pneumatic vehicle brake system andmore particularly to a control valve which regulates various operatingmodes of the brake system.

The invention is particularly applicable to a truck tractor equippedwith spring-set actuators and operated either coupled to or uncoupledfrom a trailer. However, it will be appreciated to those skilled in theart that the invention may have broader applications and in particularis applicable to tractor brake systems which do not employ spring-setactuators.

l-leretofore, truck tractors commonly employed a manually operable parkvalve which was actuable in an applied position to vent the tractorbrakes and in a released position to re-establish appropriate fluidcommunication to permit normal brake operation. Generally, there were noprovisions for setting the trailer brakes with the same control. Airsupplied to the trailer passed through a tractor protector valve whichwas automatically actuated when a loss of air pressure occurred in thetrailer system to prevent fluid communication between the tractor andtrailer brake systems. Such valves were equipped with a manual lock topermit operation of the tractor when not coupled to a trailer in thebobtail mode. Recent federal safety regulations now require the tractorbe equipped with only one valve which will simultaneously release andapply the parking brakes for both tractor and trailer. Modifications toexisting tractor systems to comply with this regulation have been toinsert the ,tractor protector valve in series with the park controlvalve. When the park control valve is applied, supply line pressure isvented and both tractor and trailer brakes are set in a park position.However, when the park control valve is placed in its released positionto resupply fluid pressure, the tractor protector valve would have to bemanually resetfBecause this would not satisfy the regulations, it hasbeen known to apply a valve with a tractor protector valve whichprevents same from automatically closing when supply line pressure isvented therethrough yet permits the valve to function normally duringhighway operation. One significant disadvantage of this arrangement isthat the tractor and trailer systems can only be pressurizedsimultaneously. Thus the trailer system could not be supplied with asource of compressed air unless the tractor brakes were released. Thismade it impractical to operate pneumatic trailer attachments such aslifts with the rigs parked as, for example, on an incline.

Another approach which permitted a source of air to be supplied to thetrailer while the tractor brakes remain set was a relatively expensivethree-valve panel cluster which required substantial modification toexisting systems to be applied thereto. This valve cluster had a firstvalve for simultaneously applying and releasing the park brakes of bothtractor and trailer to comply with the regulations. A second valvepermitted only the tractor brakes to be applied thereby permitting thetrailer system to be filled for operation of the pneumatic trailerattachments. A third valve was provided to manually shut off the airsupply to thetrailer for bobtail operation and incorporated an automaticfeature to close off the trailer air supply in event of a breakaway.

Unfortunately, the third valve also controlled the setting of thetrailer brakes with the result that the arrangement could not beconsidered foolproof in that the operator could apply the wrong valve incertain driving situations which could cause trailer jackknifing, etc.

It is thus an object of the subject invention to provide a failsafe,foolproof control valve in an air brake system which,*among otherfeatures, provides a supply of compressed air to a trailer coupled to atractor while the tractor brakes remain in a parked position.

This object along with other features of the subject invention isachieved by means of an air control valve applied in a conventional airbrake system of a tractor. The tractor brake system may be defined asincluding a conventional source of compressed air, spring-set rearservice brake actuators on a tractor, conventional coupling meanswhereby the tractor may be operated connected to or disconnected from atrailer and a conventional park control valve. The park valve isconnected in the usual manner with its inlet in fluid communication witha source of compressed air, an outlet connected to the brake actuatorsand a vent and is manually operable from a released positioncommunicating the inlet with the outlet to an applied positioncommunicating the outlet with the vent whereby the brake actuators areset in a parked position.

The control valve supplied with the system has a first port in constantfluid communication with the source of compressed air, a second port influid communication with the trailer coupling means, a third port influid communication with the outlet of the park control valve and afourth port vented to atmosphere. Fluid communication between thevarious ports is controlled by a manually actuated second plunger and apressure sensitive first plunger disposed within the valve. In thevalves normal operating mode which occurs with the park control valve ina released position, the third port is communicated with the secondport. When the park valve is applied, the control valve automaticallycycles to its park mode where the trailer system is vented to apply thetrailer brakes by movement of the first plunger which communicates thesecond and fourth ports with one another. When it is desired topressurize the trailer system or operate air driven trailer accessorieswith the tractor in its parked position and with tractor brakes set, thesecond plunger of the control valve is manually depressed to its fillmode position to establish fluid communication between the first andsecond ports. When the rig is desired to be driven in normal operation,movement of the park control valve to its released positionautomatically recycles the control valve to its normal operating mode.Alternatively, the rig could be moved from its parked position byrelease of the park valve without the control valve being first placedin its fill mode to satisfy federal regulations.

In accordance with another feature of the subject invention, the controlvalve could be applied in new systems to obviate the need of a tractorprotector control valve. This results because the control valve isdesigned to function automatically in a failsafe mode and in a manuallylocked bobtail mode. In the event of trailer system pressure loss, thevalve automatically moves to a failsafe mode by first plunger movementwhich vents the second port to atmosphere via the fourth port andprevents fluid communication between the first and/or third port withthe second port. The

tractor air system is also completely protected when the tractor isdriven not coupled to the trailer by rotation of the second plunger to alocked bobtail mode which vents the second port to atmosphere throughthe fourth port and prevents fluid communication between the firstand/or third port with either the second or fourth port.

It is thus another object of the subject invention to provide an aircontrol valve for use in a pneumatic brake system which provides variousfluid communications in accordance with a normal operating mode, a fillmode, a bobtail mode and a failsafe mode of valve operation.

Another object of the subject invention is to provide an air controlvalve which may be easily incorporated in known tractor air brakesystems for governing in a predetermined manner certain functions ofsuch systems.

Yet another object of the subject invention is to provide a controlvalve in conventional tractor brake systems which obviates the need fortractor protector control valves conventionally associated with suchsystems.

Yet another object of the subject invention is to provide a four-portvalve having two plungers operatively associated with one anotherwhereby axial movements of one plunger relative the other establishesvarious flow paths through the valve and rotational movement of oneplunger results in axial movement of the other to a locked position.

The invention may take physical form in certain parts and arrangement ofparts, a preferred embodiment of which will be described in detailherein and illustrated in the accompanying drawings which will form apart hereof and wherein:

FIG. 1 is a schematic illustration of a typical air brake systememploying the control valve of the subject invention;

FIGS. 2, 3 and 4 are sectional elevation views of the valve in variousoperating modes;

FIG. 5 is a cross-sectional view of the valve taken along line 55 ofFIG. 2; and

FIG. 6 is a top view of the control valve showing the manually operablepositions of the valve.

Referring now to the drawings wherein the showings are for the purposeof illustrating a preferred embodiment of the invention only and not forthe purpose of limiting same, FIG. 1 is a general arrangement of avehicle braking system which more specifically includes a truck tractorbrake system operable either coupled to or uncoupled from a trailerbrake system. Included in the tractor brake system is an air controlvalve 10 of the subject invention. With the exception of air controlvalve 10, the component parts shown in FIG. 1 and the overall systemfunctions, except as controlled by valve 10, are conventional. Thus thecontrol valve of the subject invention may best be explained by firsthaving ref erence to the conventional components of the system whichwill not be described in detail herein.

The conventional aspects of the system thus shown in FIG. 1 include asource of compressed air supplied by the components shown within dottedenclosure 12. Such components include, generally speaking, a compressor14 driven by the tractor engine to supply air at a given pressurecontrolled by governor 16 into a reservoir arrangement 18. Reservoir 18is capable of maintaining air supplies at supply or emergency pressurefor brake system purposes which are associated with such terms as knownin the art. An outlet line 20 from the reservoir 18 communicates with aknown treadle valve 21. Depressing treadle 21 varying degrees admits airat corresponding pressures into the service brake chambers of frontbrake actuators 24 and rear spring-set brake actuators 25 via lines 26,27 respectively and release of the treadle permits air flow to reverseits direction and vent through treadle valve 21. When the brake chambersare pressurized, an actuator plunger rod 28 is moved to actuate slackadjuster mechanisms 29 to apply the brakes during normal operating modesof the tractor. In communication with line 26, as by a suitableT-connection, is an operating or signal line 30 which, along with anemergency or supply line 31, is connected to a customary tractorprotector valve 33. Protector valve 33 consists of a usual spool-shuttleplunger which is raised by air pressure in supply line 31 to permit flowthrough line 30 of the valve and which drops to prevent flow if supplypressure falls below a predetermined value. Downstream of protectorvalve 33 signal and supply lines 30, 31 are provided with suitableconnections 34, 35 respectively or coupling means for trailer operation.

When the tractor and trailer connections 34, 35 are coupled, the trailerbrake system becomes part of the overall brake system. Most currenttrailer brake systems employ some form of emergency relay valve which isoperable to set the trailer brakes when supply line pressure drops belowa predetermined value and return the brakes to normal operating modewhen supply pressure is restored. The conventional trailer systemillustrated in FIG. 1 includes an emergency relay valve 40 which isconnected to signal and supply lines 30, 31, a reservoir 41 and trailerbrake actuators 43 through suitable lines 44. Trailer brake actuators 43are shown to be of the single diaphragm, air appliedspring released typealthough other brake actuators may be applied to the trailer system ifslight changes, known to those skilled in the art, be made in the fluidcommunication lines. Independent of the brake actuators employed,emergency relay valve 40 functions in the usual manner to admitreservoir pressure to brake actuators 43 when treadle valve 21 isdepressed and vent same when the treadle is released. Similarly in theevent of a predetermined pressure drop in supply line 31, relay valve 40is actuated to supply air at system pressure from reservoir 41 totrailer brake actuators 43 to set the brakes. When supply pressure isrestored in line 31, relay valve 40 vents the air in the trailer brakeactuators 43 to re-establish normal operating mode of the system.

Venting of supply line 31 to actuate the trailer brakes to a parkedposition is controlled by a park brake control valve 46 in the tractorcab. Park brake control 46 has an inlet connected by a suitable line 48to the source of compressed air 12, a vent 49 and an outlet which isconnected to a line 50 which in turn leads to one of the ports of theair control valve 10 of the subject invention. The outlet of the parkbrake control valve 46 is also connected by a line 51 to the rearspring-set brake actuator 25. The spring-set brake actuator 25illustrated is of a known type having a first diaphragm 53 connected totreadle valve 21 through line 27 which is movable under pressure to setthe brakes during normal operation of the tractor, and a seconddiaphragm 54 movable under pressure to maintain a powerful spring 55 ina compressed manner. Second diaphragm 54 is in fluid communication withline 51 and when park valve 46 is in its released position, air atsupply line pressure is communicated from line 48 to line 51 to maintainspring 55 compressed. When park valve 46 is in its applied position,lines 50, 51 are vented to atmosphere by the park valve vent 49 andspring 55 in spring-set actuator 25 is released from its compressedposition to axially move plunger rod 28 to set the rear brakes.

Having thus described the conventional aspects of the brake systemillustrated, the structure and operation of air control valve will nowbe described in detail. As shown in FIG. 1, the air control valve 10 hasfour ports which are physically connected within the above describedsystem as follows:

I. A first port 60 on the inlet side of the valve communicates with thesource of compressed air 12 upstream of park control valve 46 by a line58 T'd to line 48. First port is thus connected to a source ofcompressed air at supply pressure.

2. A second port 61 on the outlet side of the valve communicates withsupply line 31 which leads to tractor protector valve 33.

3. A third port 62 is connected downstream of park control valve 46 tothe source of compressed air 12 at supply line pressure by line 50.

4. A fourth port 63 is vented to atmosphere.

Referring now to FIG. 2, air control valve 10 may best be defined ashaving a first valve body portion 70 and a second valve body portion 71.Within first valve body portion 70 is a first valve chamber 72 in fluidcommunication with third and fourth ports 62, 63. Within second valvebody portion 71 is a second valve chamber 73 in fluid communication withfirst and second ports 60, 61. Both valve chambers 72, 73 are in fluidcommunication and generally perpendicular to one another. It should benoted though that first chamber 72 is axially shifted from center withrespect to second chamber 73 to minimize valve length as will beexplained hereafter.

Slidingly and sealingly disposed within first valve chamber 72 is anaxially extending first plunger 76. To permit assembly of first plunger76 within first valve chamber 72, the fourth valve port 63 is shown as acap or plug 77 threaded into first valve portion 70. Slidingly andsealingly disposed within second valve chamber 73 is a second plunger79. To permit assembly of second plunger 79 within second chamber 73,valve body portions 70, 72 are formed from separate pieces which aresuitably secured together by known means and sealed as at 80. Forpurposes of nomenclature and ease of explanation, the upwardly extendingpart 81 of first valve body portion 70 shown in FIG. 1 is defined tocomprise a portion of second valve chamber 73.

First plunger 76 has a first slider-piston 83 at one end thereof, asecond slider-piston 84 at the opposite end and a relatively smallinterconnecting rod 85 joining slider-pistons 83, 84 together with a gap86 therebetween. First slider-piston 83 is defined by a cylindricallyshaped sliding portion 87 adjacent interconnecting rod 85 and a smallercylindrical piston portion 88 extending from sliding portion 87. Whenfirst plunger 76 is axially moved to its first position as shown inFIGS. 3 and 4, first piston portion 88 abuts third port 62 and firstsliding portion 87 is sealed and maintained in position by an O-ring 89positioned within an annular groove 90 formed in first valve chamber 72.Similarly, second slider-piston 84 has a second sliding portion 91 and asecond piston portion 92; second piston portion 92 abutting fourth port63 and second sliding portion 91 sealingly engaged by a second O-ringseal 93 when first plunger 76 is in its second position as shown in FIG.2. However, second slider-piston 84 has a V- shaped groove notched inits sliding portion 91 adjacent piston portion 92 to permit fluid flowaround second slider-piston 84 when first plunger 76 is in its firstposition. First plunger 76 is normally biased towards its first positionby spring means shown to include a first spring 96 mounted between plug77 and second slider portion 91 and a second spring 97 compressed at oneend by plug 77 and received within second piston portion 92 which ishollowed in a customary manner to seat spring 97 therein (see FIGS.3,4).

Second valve chamber 73 is in fluid communication with first valvechamber 72 at its bottom end and is open at its top end and may properlybe viewed as a stepped cylindrical bore having a first cavity 99adjacent first chamber 72 which is larger in area than a second cavity100 which is defined to include the open end of second valve chamber 73.First cavity 99 is especially configured and includes a shelf or a stop101 which is physically located at the bottom of first cavity 99 todefine a line of demarcation between the first and second valve chambers72, 73. Shelf 101 may be viewed as being shaped as a half moon andextending within first cavity 99 to a distance not beyond the centerline102 thereof. As best shown in FIG. 5, shelf 101 is in turn relieved asat 103 to define a half-moon shaped or other suitable open receivingarea 104 for purposes to be explained hereafter. Shelf 101 may thus beviewed as a segmented ring extending from first cavity 99. Alsoextending with first cavity 99 adjacent second port 61 is a shoulder 107which functions as a second stop for second plunger 79 and defines aline of demarcation between first and second cavities 99, 100. Inbetween shoulder 107 and shelf 101 are a series of circumferentiallyspaced flutes 108 which are cut into first cavity 99, axially extendalong the cavity a predetermined distance and are open at their upperends to provide communication with second port 61.

Second plunger 79 which is disposed within second valve chamber 73 issimilarly stepped in cylindrical configuration to define a first plungerportion 110 disposed within first cavity 99 and a smaller second plungerportion 111 disposed within second cavity 100. Second plunger portion 111 is recessed as at 113 to define a flow area 114 which is always incommunication with first port 60. Flow area 114 is adapted to be sealedfrom other valve ports by O-rings 115, 116 received within groovesformed in second plunger portion 111 and positioned above and belowrecess 113. Second plunger portion 111 blends into the larger firstplunger portion 110 by means of a flange or frusto-conical surface 118which surface is adapted to engage shoulder 107 for preventing movementof second plunger 79 out of second chamber 73. Disposed directly belowfrustoconical surface 1 l8 and within a groove formed in first plungerportion 1 10 is an O-ring seal 119 which is operable, depending upon theposition of second plunger 79 within second chamber 73, to preventcommunication between first and second chambers 72, 73. The base orbottom of second plunger portion 111 may be viewed as a generally flatsurface 120 from which a semicircular boss 121 depends. Depending fromboss 121 at some predetermined distance from centerline 102 is anactuating lever 123. Lever 123 extends within the gap 86 between slidingportions 87, 91 of first plunger 76. When frusto-conical surface 118 ofsecond plunger 79 contacts shoulder 107 as shown in FIG. 2, actuatinglever 123 moves as an eccentric as shown in FIG. into the opening 104 inshelf 101. Simultaneously, actuating lever 123 contacts sliding portion87 to lock first sliding piston 83 into the position shown in FIG. 3.

As best shown in FIG. 5, cavity 99 is offset from the center of chamber72. This permits lever 123 to drop below connecting rod 85 when thevalve is in the position shown in FIG. 4. This permits the length ofsecond plunger 79 to be shorter than what it otherwise might be to makethe valve compact.

To effect manual movement, both rotary and axial, of second plunger 79to establish various mode positions of valve 10, a stud 125 extendingbeyond the valve body may be provided as a part of the second plunger.An operating handle 126 as shown in FIG. 6

may thus be applied to stud 125 and an index dial 127 may be affixed tothe valve body in any known manner. To provide positive stop for thevalve to assure operator feel a suitable detent arrangement may beprovided such as might easily suggest itself to those skilled in the artand not shown herein, although valves made TABLE I 1st 2nd 3rd 4thOperating Mode Port Fort Port Port Normal Highway Sealed X X SealedFailsafe (Automatic) Sealed X Sealed X Park Sealed X Sealed X Fill X XSealed Sealed Bobtail (Manual Lock) Sealed X Sealed X X" indicates fluidcommunication therebetween.

The normal operating highway mode occurs with the trailer coupled to thetractor and park valve 46 in a released position to thus supply air atsupply pressure into third port 62. Air at supply pressure also existsin first port 60. Referring now to FIG. 2, the air pressure at thirdport 62 opposes first and second springs 96, 97 to compress same andmove first plunger 76 into its second position whereby the secondslider-piston thereof 84 prevents leakage to atmosphere through port 63because sliding portion 91 is sealed by O-ring 93. Air then travels pastfirst slider-piston 83 and acts against the base surface 120 (includingboss 121) of second plunger 79 to move same upward in second chamber 73until frusto-conical surface 118 contacts shoulder 107 to preventfurther movement of the second plunger. Air then flows through flutes108 into second port 61 and thence through line 31, etc. First port 60is isolated by seals 115, 116.

Control valve 10 when in its normal operating mode automatically shiftsto its failsafe mode if a loss of fluid pressure should occur in thetrailer air system as, for example, if the trailer or towed vehicleshould break away or if any other serious leak should develop. Theoccurrence of such leakage would drop the pressure entering third port62. When this pressure drops below the force at which springs 96, 97 arecompressed (and this value may be varied for different applications byappropriate spring rates) first slider-piston 83 will move to its firstposition to prevent any air from escaping through third port 62.Simultaneously, second slider-piston of the first plunger willautomatically uncover the fourth vent port 63 thus venting supply line31 through second port to atmosphere. Second plunger 79 will not dropdownward insecond chamber 73 because pressure isolated port 60 bearsagainst seals 115, 116. Seals 115, 116 in turn press against secondcavity to not only maintain second plunger 79 in the position but alsoprovide feel" to the operator when manually shifting the valve. Aparticular advantage of this valve is that subsequent pressure buildupabove the preselected spring force value will reverse the above sequenceand re-establish normal highway operating mode. Thus the failsafefeature of valve 10 is also foolproof.

Setting the trailer brakes for park position automatically occurs whenpark control valve 46 is moved to its applied position which opens lines50, 51 to atmosphere. When the pressure in third port 62 reaches apredetermined value as it exhausts to atmosphere, springs 96, 97 forcefirst slider-piston 83 of first plunger 76 to seal third port 62.Simultaneously, the second port is connected via flutes 108, second andfirst chambers 72, 73 to atmosphere through fourth port 63. This actionsets the brakes of trailers which are in common use at this time, andsatisfies federal requirements that setting of both tractor and trailerbrakes be accomplished by one valve.

From the parked position thus described, the trailer air reservoir 41can be pressurized prior to moving the rig and importantly withoutreleasing spring-set brake actuators 25 on the tractor by simply pushingsecond plunger 79 downwardly from its position shown in FIG. 2 to itsfill position shown in FIG. 4. That is, the second plunger is pusheddownwardly until its base portion contacts the top of shelf 101. In thisposition, 0- ring 119 prevents first and second ports 60, 61 "fromcommunicating with second valve chamber 73 while permitting air atsupply pressure in first port 60 to communicate through flow area 114 tosecond port 61. When it is desired to operate the rig in normal highwayoperation, movement of part control 46 to its released position suppliesair at supply pressure to third port 62. This pressure forces the firstplunger to move towards its second position and acts against base120,121 of the second plunger 79 to move same to its normal highwayposition as shown in FIG. 2. The second plunger 79 will move in thismanner because the area at the base thereof is larger than the area ofthe second plunger portion 111 which is acted upon by air pressure fromfirst port 60. In this connection, it should be noted that control valve10 of the subject invention is foolproof in the sense that if theoperator failed to actuate the valve in its fill mode and simplyreleased park brake 46, the valve would revert to the position shown inFIG. 2 and the trailer reservoir 41 would be pressurized although thetractor spring-set brakes 25 would be simultaneously released. Thecontrol valve is also foolproof in the sense that if the rig wasoperating with valve 10 in normal mode and the operator attempted toplace the valve in fill mode, it would simply pop back to normal mode.Finally upon either method of releasing'the parked brakes, federalregulations are satisfied in that actuation of a single park controlvalve 46 accomplishes same. i a

Finally, the tractor brake systemis cornpl'etely protected by controlvalve 10 'when the valve is placed in its bobtail operating modeposition for operation of the tractor not coupled to a trailer. This issimply accomplished by rotating second plunger 79 one half 'turn fromits normal highway position shown in FIG. 2. As best shown in FIGS. 3and 5, this rotation causes actuation lever 123 to be received withinthe relieved area of shelf 10l. Simultaneously, the actuating lever 123locks first plunger 76 into its first position to seal third port 62,vent second port 61 to atmosphere via fourth port 63 and isolate thefirst port 60 by seals 115, 116. With the valve in the bobtail positionshown in FIG. 3, it should be noted that the bottom of boss 121 isseated against the top of shelf 101 to prevent O-ring 119 from droppingbelow flutes 108. Thus, it is impossible to prevent second port 61 frombeing vented to atmosphere. Additionally, because control valve 10 mustbe rotated into its bobtail mode, it is believed that the operator willbecome better aware of such valve position since most valves in suchsystems are push-pull applications. If desired, protrusions may beprovided on second plunger 79 (not shown) to provide solid rotationalstops. Furthermore, the failsafe and bobtail modes of the control valve10 are functional equivalents of known tractor protector control valves.Thus, brake systems need not be equipped with such valves and animproved system which complies with federal regulations may be had atless cost.

The invention has thus been described with reference to a preferredembodiment, i.e., control valve 10 within a conventional tractor-trailerair system. Obviously, modifications and alterations will occur toothers, upon reading and understanding the specification, It is myintention to include all such modifications and alterations insofar asthey come within the scope of the present invention.

It is thus the essence of the invention to provide a control valve foruse in pneumatic braking systems which incorporates a pressure sensitivefirst plunger in conjunction with a manually movable second plungerwhich operate in phased relationship with one another to permit thebrake system to satisfactorily function in a wide variety of operatingphase relationships.

Having thus defined the invention, 1 claim:

1. A control valve for use in a brake system comprising:

a valve body having a first chamber in a first portion thereof and asecond chamber in a second portion thereof, said second chamber open atone end and in communication with said first chamber at its oppositeend;

a first and second port in communication with said second chamber and athird and fourth port in communication with said first chamber;

a first pressure responsive plunger slidably disposed within said firstchamber, first sealing means asso ciated with said first plungerpreventing fluid coma second plunger within said second chambermovable"between a first and seeond position, second sealing m ean'sassociated with said second plunger to isolate said first port fromfluid communication with said se cond port and said first chamber andprovide fluid communication between said second 4 port and said'firstchamber when said second plunger is in a first position, third sealingmeans associated with said second plunger to prevent fluidcommunication" between said first and second chambers and provide fluidcommunication between said first and second ports when said plunger isin said second position.

2. The control valve of claim 1 further including spring meansassociated with said first plunger normally biasing said first plungerto said first position; and

pressure responsive means formed as part of said second plunger andoperable to automatically move said second plunger from its secondposition to its first position when said bias of said spring means isneutralized.

3. The control valve of claim 2 wherein said second chamber is furtherdefined by a first cavity adjacent said first chamber, and a secondcavity adjacent said open end of said second chamber and contiguous withsaid first cavity, said first cavity greater in cross section than saidsecond cavity;

said second plunger is further defined by a first portion similar inconfiguration to said first cavity and a second portion similar inconfiguration to said second portion, said first portion having a basesurface adjacent said second chamber; and

said pressure responsive means including said base surface, and anactuating lever associated therewith.

4. The control valve of claim 3 wherein said first plunger includes afirst slider-piston adjacent said third port, a second slider-pistonadjacent said fourth port and a member interconnecting said first andsecond slider-pistons and defining a gap therebetween, said actuatinglever extending within said gap.

5. The control valve of claim 4 wherein each slider-piston includes acylindrical slider portion adjacent said member and a cylindrical pistonportion extending from said slider portion, said first slider portionsealingly slidably supported by a first seal in said first chamber whensaid first plunger is in its first position, said second slider portionsealingly and slidably supported in said first chamber by a second sealwhen said first plunger is in its second position; and

said second slider portion having a groove formed adjacent said secondpiston portion to provide fluid communication between said fourth portand said second chamber when said first plunger is in its firstposition.

6. The control valve of claim 5 wherein an annular shoulder extendingfrom said second chamber adjacent said second port defines a line ofdemarcation between said first and second cavities,

said second plunger abutting said shoulder when said second plunger isin its second position; and

said first cavity further having a plurality of circumferentially spacedflutes communicating with said second port, said flutes extending apredetermined axial distance within said first cavity to provide fluidcommunication between said first cavity and said second port when saidsecond plunger is in its first position.

7. The control valve of claim 6 further including said first and secondcavities, and said first and second portions of said second plungerbeing generally cylindrical in configuration; and

eccentric means associated with saidbase surface operable when saidsecond plunger in its first position is rotated to lock said firstplunger in its first position.

8. The control valve of claim 7 wherein said cavity includes a shelfprotruding therefrom adjacent said first chamber, said shelf recessed todefine a central opening therein; and

said eccentric means includes a boss depending from said base surfaceand extending on one side of the center of said first cavity and anactuating lever depending from said boss, said actuating lever receivedwithin said central opening and said boss resting on said shelf whensaid second plunger is rotated, said boss preventing rotation when saidsecond plunger is in second position while permitting rotation when saidsecond plunger is in its first position.

1. A control valve for use in a brake system comprising: a valve bodyhaving a first chamber in a first portion thereof and a second chamberin a second portion thereof, said second chamber open at one end and incommunication with said first chamber at its opposite end; a first andsecond port in communication with said second chamber and a third andfourth port in communication with said first chamber; a first pressureresponsive plunger slidably disposed within said first chamber, firstsealing means associated with said first plunger preventing fluidcommunication between said third port and said second chamber when saidfirst plunger is in a first position and preventing communicationbetween said fourth port and said second chamber when said plunger is ina second position; and a second plunger within said second chambermovable between a first and second position, second sealing meansassociated with said second plunger to isolate said first port fromfluid communication with said second port and said first chamber andprovide fluid communication between said second port and said firstchamber when said second plunger is in a first position, third sealingmeans associated with said second plunger to prevent fluid communicationbetween said first and second chambers and provide fluid communicationbetween said first and second ports when said plunger is in said secondposition.
 2. The control valve of claim 1 further including spring meansassociated with said first plunger normally biasing said first plungerto said first position; and pressure responsive means formed as part ofsaid second plunger and operable to automatically move said secondplunger from its second position to its first position when said bias ofsaid spring means is neutralized.
 3. The control valve of claim 2wherein said second chamber is further defined by a first cavityadjacent said first chamber, and a second cavity adjacent said open endof said second chamber and contiguous with said first cavity, said firstcavity greater in cross section than said second cavity; said secondplunger is further defined by a first portion similar in configurationto said first cavity and a second portion similar in configuration tosaid second portion, said first portion having a base surface adjacentsaid second chamber; and said pressure responsive means including saidbase surface, and an actuating lever associated therewith.
 4. Thecontrol valve of claim 3 wherein said first plunger includes a firstslider-piston adjacent said third port, a second slider-piston adjacentsaid fourth port and a member interconnecting said first and secondslider-pistons and defining a gap therebetween, said actuating leverextending within said gap.
 5. The control valve of claim 4 wherein eachslider-piston includes a cylindrical slider portion adjacent said memberand a cylindrical piston portion extending from said slider portion,said first slider portion sealingly slidably supported by a first sealin said first chamber when said first plunger is in its first position,said second slider portion sealingly and slidably supported in saidfirst chamber by a second seal when said first plunger is in its secondposition; and said second slider portion having a groove formed adjacentsaid second piston portion to provide fluid communication between saidfourth port and said second chamber when said first plunger is in itsfirst position.
 6. The control valve of claim 5 wherein an annularshoulder extending from said second chamber adjacent said second portdefines a line of demarcation between said first and second cavities,said second plunger abutting said shoulder when said second plunger isin its second position; and said first cavity further having a pluralityof circumferentiAlly spaced flutes communicating with said second port,said flutes extending a predetermined axial distance within said firstcavity to provide fluid communication between said first cavity and saidsecond port when said second plunger is in its first position.
 7. Thecontrol valve of claim 6 further including said first and secondcavities, and said first and second portions of said second plungerbeing generally cylindrical in configuration; and eccentric meansassociated with said base surface operable when said second plunger inits first position is rotated to lock said first plunger in its firstposition.
 8. The control valve of claim 7 wherein said cavity includes ashelf protruding therefrom adjacent said first chamber, said shelfrecessed to define a central opening therein; and said eccentric meansincludes a boss depending from said base surface and extending on oneside of the center of said first cavity and an actuating lever dependingfrom said boss, said actuating lever received within said centralopening and said boss resting on said shelf when said second plunger isrotated, said boss preventing rotation when said second plunger is insecond position while permitting rotation when said second plunger is inits first position.